Posted Updated 8 minutes read (About 1249 words)

libcurl上傳圖片

快速產生libcurl程式碼

首先先用curl指令發送request，確認可以發送成功後可以用指令自動產生程式碼，在這裡我們將上傳一張圖片到http server，利用curl讀取電腦的圖片並且上傳

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curl -X POST "http://localhost:8000/upload" -H "accept: application/json" -H "Content-Type: multipart/form-data" -F "uploadedFile=@a.jpg;type=image/jpeg" -F "EventTime=2022-01-01"

利用curl的--libcurl選項就可以快速產生c語言的程式碼，程式碼會被儲存到code.c

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curl -X POST "http://localhost:8000/upload" -H "accept: application/json" -H "Content-Type: multipart/form-data" -F "uploadedFile=@a.jpg;type=image/jpeg" -F "EventTime=2022-01-01" --libcurl code.c

產生的程式碼如下

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/********* Sample code generated by the curl command line tool **********
 * All curl_easy_setopt() options are documented at:
 * https://curl.haxx.se/libcurl/c/curl_easy_setopt.html
 ************************************************************************/
#include <curl/curl.h>

int main(int argc, char *argv[])
{
  CURLcode ret;
  CURL *hnd;
  curl_mime *mime1;
  curl_mimepart *part1;
  struct curl_slist *slist1;

  mime1 = NULL;
  slist1 = NULL;
  slist1 = curl_slist_append(slist1, "accept: application/json");
  slist1 = curl_slist_append(slist1, "Content-Type: multipart/form-data");

  hnd = curl_easy_init();
  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);
  curl_easy_setopt(hnd, CURLOPT_URL, "http://localhost:8000/upload");
  curl_easy_setopt(hnd, CURLOPT_NOPROGRESS, 1L);
  mime1 = curl_mime_init(hnd);
  part1 = curl_mime_addpart(mime1);
  curl_mime_filedata(part1, "a.jpg");
  curl_mime_name(part1, "uploadedFile");
  curl_mime_type(part1, "image/jpeg");
  part1 = curl_mime_addpart(mime1);
  curl_mime_data(part1, "2022-01-01", CURL_ZERO_TERMINATED);
  curl_mime_name(part1, "EventTime");
  curl_easy_setopt(hnd, CURLOPT_MIMEPOST, mime1);
  curl_easy_setopt(hnd, CURLOPT_HTTPHEADER, slist1);
  curl_easy_setopt(hnd, CURLOPT_USERAGENT, "curl/7.68.0");
  curl_easy_setopt(hnd, CURLOPT_MAXREDIRS, 50L);
  curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, (long)CURL_HTTP_VERSION_2TLS);
  curl_easy_setopt(hnd, CURLOPT_SSH_KNOWNHOSTS, "/home/ai_server/.ssh/known_hosts");
  curl_easy_setopt(hnd, CURLOPT_CUSTOMREQUEST, "POST");
  curl_easy_setopt(hnd, CURLOPT_FTP_SKIP_PASV_IP, 1L);
  curl_easy_setopt(hnd, CURLOPT_TCP_KEEPALIVE, 1L);

  /* Here is a list of options the curl code used that cannot get generated
     as source easily. You may select to either not use them or implement
     them yourself.

  CURLOPT_WRITEDATA set to a objectpointer
  CURLOPT_INTERLEAVEDATA set to a objectpointer
  CURLOPT_WRITEFUNCTION set to a functionpointer
  CURLOPT_READDATA set to a objectpointer
  CURLOPT_READFUNCTION set to a functionpointer
  CURLOPT_SEEKDATA set to a objectpointer
  CURLOPT_SEEKFUNCTION set to a functionpointer
  CURLOPT_ERRORBUFFER set to a objectpointer
  CURLOPT_STDERR set to a objectpointer
  CURLOPT_HEADERFUNCTION set to a functionpointer
  CURLOPT_HEADERDATA set to a objectpointer

  */

  ret = curl_easy_perform(hnd);

  curl_easy_cleanup(hnd);
  hnd = NULL;
  curl_mime_free(mime1);
  mime1 = NULL;
  curl_slist_free_all(slist1);
  slist1 = NULL;

  return (int)ret;
}
/**** End of sample code ****/

將curl_mime_filedata改成curl_mime_data

由於我的目的是將在記憶體中已經被encode好的圖片直接上傳，所以要用curl_mime_data
直接上傳記憶體內的內容。
注意除了用curl_mime_data放入資料以外，還必須自己手動把Content-Disposition補上filename。
另外記得curl_mime_data不可以用CURL_ZERO_TERMINATED而是要實際算出圖片的資料長度。
可以參考官方的範例

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curl_mime *mime;
curl_mimepart *part;

/* create a mime handle */
mime = curl_mime_init(easy);

/* add a part */
part = curl_mime_addpart(mime);

/* send image data from memory */
curl_mime_data(part, imagebuf, imagebuf_len);

/* set a file name to make it look like a file upload */
curl_mime_filename(part, "image.png");

/* set name */
curl_mime_name(part, "data");

讀binary file

直接將圖片讀進記憶體內不要做任何處理
範例

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void ReadFile(char *name)
{
	FILE *file;
	char *buffer;
	unsigned long fileLen;

	//Open file
	file = fopen(name, "rb");
	if (!file)
	{
		fprintf(stderr, "Unable to open file %s", name);
		return;
	}
	
	//Get file length
	fseek(file, 0, SEEK_END);
	fileLen=ftell(file);
	fseek(file, 0, SEEK_SET);

	//Allocate memory
	buffer=(char *)malloc(fileLen+1);
	if (!buffer)
	{
		fprintf(stderr, "Memory error!");
                                fclose(file);
		return;
	}

	//Read file contents into buffer
	fread(buffer, fileLen, 1, file);
	fclose(file);

	//Do what ever with buffer

	free(buffer);
}

termshark

再除錯的過程中，最好可以直接看一看自己的封包長什麼樣子，對於沒有螢幕的Ubuntu Server，可以安裝termshark，它可以做到跟wireshark差不多的事情

完整範例

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/********* Sample code generated by the curl command line tool **********
 * All curl_easy_setopt() options are documented at:
 * https://curl.haxx.se/libcurl/c/curl_easy_setopt.html
 ************************************************************************/
#include <curl/curl.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char *argv[])
{
  CURLcode ret;
  CURL *hnd;
  curl_mime *mime1;
  curl_mimepart *part1;
  struct curl_slist *slist1;

  mime1 = NULL;
  slist1 = NULL;
  slist1 = curl_slist_append(slist1, "accept: application/json");
  slist1 = curl_slist_append(slist1, "Content-Type: multipart/form-data");

  hnd = curl_easy_init();
  curl_easy_setopt(hnd, CURLOPT_BUFFERSIZE, 102400L);


    curl_easy_setopt(hnd, CURLOPT_URL, "http://localhost:8000/upload");


  curl_easy_setopt(hnd, CURLOPT_NOPROGRESS, 1L);
  mime1 = curl_mime_init(hnd);
  part1 = curl_mime_addpart(mime1);


    // https://www.w3schools.blog/c-read-binary-file
    FILE *file;
    const char *buffer;
    unsigned long fileLen;

    //Open file
    file = fopen("image.jpg", "rb");
    if (!file)
    {
      fprintf(stderr, "Unable to open file");
      return;
    }

    //Get file length
    fseek(file, 0, SEEK_END);
    fileLen=ftell(file);
    fseek(file, 0, SEEK_SET);

    //Allocate memory
    buffer=(char *)malloc(fileLen+1);
    if (!buffer)
    {
      fprintf(stderr, "Memory error!");
                                  fclose(file);
      return;
    }

    //Read file contents into buffer
    fread(buffer, fileLen, 1, file);
    fclose(file);

    /* add data to the part  */
    curl_mime_data(part1, buffer, fileLen);

    /* set a file name to make it look like a file upload */
    curl_mime_filename(part1, "image.jpg");
    
    free(buffer);


  curl_mime_name(part1, "uploadedFile");
  curl_mime_type(part1, "image/jpeg");
  part1 = curl_mime_addpart(mime1);
  curl_mime_data(part1, "2022-02-02", CURL_ZERO_TERMINATED);
  curl_mime_name(part1, "EventTime");
  curl_easy_setopt(hnd, CURLOPT_MIMEPOST, mime1);
  curl_easy_setopt(hnd, CURLOPT_HTTPHEADER, slist1);
  curl_easy_setopt(hnd, CURLOPT_USERAGENT, "curl/7.68.0");
  curl_easy_setopt(hnd, CURLOPT_MAXREDIRS, 50L);
  curl_easy_setopt(hnd, CURLOPT_HTTP_VERSION, (long)CURL_HTTP_VERSION_2TLS);
  curl_easy_setopt(hnd, CURLOPT_CUSTOMREQUEST, "POST");
  curl_easy_setopt(hnd, CURLOPT_FTP_SKIP_PASV_IP, 1L);
  curl_easy_setopt(hnd, CURLOPT_TCP_KEEPALIVE, 1L);


  ret = curl_easy_perform(hnd);

  curl_easy_cleanup(hnd);
  hnd = NULL;
  curl_mime_free(mime1);
  mime1 = NULL;
  curl_slist_free_all(slist1);
  slist1 = NULL;

  return (int)ret;
}
/**** End of sample code ****/

參考:

https://daniel.haxx.se/blog/2022/09/12/convert-a-curl-cmdline-to-libcurl-source-code/

https://curl.se/libcurl/c/curl_mime_filename.html

https://geekscripts.guru/termshark-terminal-ui-for-tshark/

libcurl上傳圖片

https://jenhaoyang.github.io/uncategorized/c9241cf759be/

Author

Steven

Posted on

2023-03-22

Updated on

2025-01-14

Licensed under

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